Method of making magnetic impulse record members



Nov. 29, 1949 M. CAMRAS ET AL 2,439,520

METHOD OF MAKING MAGNETIC IMPULSE RECORD MEMBERS Filed Aug. 7, 1947 2Shets-Sheet 1 RESIDUAL MAGNETI sm GAUSS APPLIED FIELD- H- OERSTEDSCOERCIVE FORCE c OERSTEDS APPLIE FlELD-H- OERSTEDS hlET'll-UZ" 5 M44? wC'mmens firm/M E fin/vases Nov. 29, 1949 M. CAMRAS ETAL METHOD OF MAKINGMAGNETIC IMPULSE RECORD MEMBERS 2 Sheets-Sheet 2 Filed Aug. 7, 1947 HIGHFREQUENCY OSCILLATOR [rm En [0F 5 Me w (:QMEJ-S f/rewv f: fin/vasesAUDIO AMPLIFIER Patented Nov. 29, 1949 METHOD OF MAKINGMAGNETIC IMPULSERECORD MEMBERS Marvin Camras, Chicago, Ill., and Hyrum E. Flanders, SaltLake City, Utah, assignors to Armour Research Foundation of IllinoisInstitute 01' Technology, Chicago, Ill., a corporation of IllinolsApplication August 7, 1947, Serial No. 767,290 5 Claims. (Cl. 148-12) 1This invention relates to a magnetic impulse record member and to amethod of making the same.

of a wire, tape, ribbon, or the like, formed of normally non-magneticstainless steel that has been cold worked to impart thereto desirablemagnetic properties.

. The present invention is a continuation-inpart of our pendingapplication Serial No. 610,678,

filed August 13, 1945.

According to our present invention, stainless steel, preferably of thetype generally referred to as 18-8 stainless steel, is formed into amagnetic impulse record member by successive series of cold workingsteps, each series being preceded in each instance by a soft annealingstep. By properly controlling the composition of the stainless steelalloy and the conditions under which the cold working and annealing iscarried out, a magnetic impulse record member can be obtained thatpossesses very desirable magnetic properties for use in magnetic soundrecorders, and the like.

We have found that the composition of the stainless steel alloy may bevaried through a considerable range with respect to the chromium andnickel content, and through a smaller range with respect to the carboncontent, provided that the elements are balanced to provide definitestability limits of the austenite toward decomposition on cold working.For instance, the chromium content can be varied between 12 and 25%, thenickel content between 5.5 and 12% and the carbon content between 0.06and 0.20%, but the nickel content should be relatively lower when thechromium content is relatively higher, and the nickel content shouldalso be lower when the carbon content is higher, at all times, however,keeping the percentages within the broad ranges just given.

With respect to the magnetic properties that are desired in a magneticsound impulse record member for use in a magnetic sound recorder, wehave found that the two most important properties to control are theresidual magnetism, Br, and the coercive force, He. The low frequencyresponse of the magnetic record member, is, in general, proportional toits Br, while its high frequency response is improved by a relativelyhigh He. Also, in order for the magnetic-impulse rec- More particularly,the invention relates 'to a magnetic impulse record member in the formord member to be relatively permanent in its retention of magneticallyrecorded impulses, it should have a relatively high coercive force.

There are other magnetic characteristics that we have found desirable inmagnetic impulse record members and that are found-in the magneticimpulse record member of our present invention.

For one thing, it is not desirable that there should be a straightlinear relationship between the applied field and the residualmagnetism, or between the applied field and the coercive force. If therewere such a linear relationship in the case of residual magnetism, amagnetized portion of the record member would tend to magnetize anadjacent unmagnetized portion of the record member, as for instance anadjacent strand of the wire in the same reel. The curve produced byplotting the residual magnetism against the applied field,

' therefore, should rise very slowly for values of acteristics are shownin the drawings.'

We have further found that in order to produce magnetic impulse recordmembers havin these desirable magnetic properties and characteristics,it is necessary to subject the stainless steel alloy from which therecord member is to be made to a series oi cold working steps in whichthe final amount of reduction in cross sectional area is at least withinthe range of between and 95%, preferably in the neighborhood of and as aresult of which the record member is reduced to a diameter or athickness preferably of not greater than about'0.005 inch. Where therecord member in its final form is a wire of circular cross section, thediameter of the wire should preferably be less than 0.005 inch andusually of the order of 0.004 inch, while if the record memberin inch.We have found that even though the composition of the alloy and thepercentage reduction effected by cold working are identical in two wiresof difierent diameters, the smaller diameter wire, if within the rangesindicated, may have magnetic properties imparted to it that render iteminently suited for use in magnetic sound recorder devices, whereas thewire of a diameter lying substantially outside of the specifieddiameters, as for instance one having a final diameter of 0.04 inch,will not attain those same desirable magnetic properties. Accordingly,the diameter, or thickness, of the magnetic impulse record member mustbe kept within the limits herein specifled for maximum development ofits desirable magnetic properties.

It is therefore an important object of this invention to provide amagnetic impulse record member having magnetic properties andcharacteristics peculiarly adapting it for use in magnetic soundrecorders and the like.

It is a further important object of this invention to provide anelongated magnetic impulse record member in the form of a wire, tape,ribbon or the like, of a diameter or thickness of the order of 0.004inch and formed of a normally non-magnetic chrome-nickel steel that hasbeen cold worked to impart thereto particularly de sirable magneticproperties.

It is a further important object of this invention to provide a methodof producing an elongated magnetic impulse record member, starting froma non-magnetic, chrome-nickel steel of such composition as to besusceptible of acquiring desirable magnetic properties upon being coldworked, and cold working the alloy to produce such magnetic properties.

It is a further important object of this invention to provide a methodof making a magnetic impulse record member from a normallynonmagneticstainless steel, the analysis of whichis controlled withincertain limits as to chromium, nickel and carbon so that the alloy iscapable of having imparted thereto the desired magnetic properties, andthen effecting the reduction of the cross-sectional area of blank ofsuch alloy by-a series of cold working steps each series being precededby a soft annealing step and including a final reduction oi between 50and 95% to produce a member having at least one dimension reduced bycold working to not greater than about 0.004 inch and possessing thedesired magnetic properties and characteristics.

Other and further important objects of this invention will be apparentfrom the disclosures in the specification and the accompanying drawings.

On the drawings:

Figure 1 is a chart of curves obtained by plotting residual magnetismagainst applied fields up to 1000 oersteds showing optimum, minimum andmaximum values of residual magnetism and showing a shaded area betweensuch curves representing residual magnetism values and characteristicsfound suitable in magnetic impulse record members of our invention.

Figure 2 is a chart of curves obtained by plotting coercive forceagainst applied fields up to 1000 oersteds, showing optimum, minimum andmaximum values of coercive force, and showing a shaded area between suchcurves representing coercive force values and characteristics foundsuitable in the magnetic impulse record member I 4 We may use as thestarting material a stainless steel alloy within the following broadranges of percentages by weight:

Per cent Chromium 12 to 25 Nickel 5.5 to 14 Carbon 0.08 to 0.20Accessory elements, (maganese,

silicon, nitrogen, titanium, columbium, molybdenum and impurities likesulphur and phosphorus) Less than 8.5

Iron. balance In general, the constituents which we prefer to vary inmaintaining the proper balance of the alloy are nickel, carbon, chromiumand iron.

Accessory elements, such as manganese, silicon and nitrogen, areordinarily held substantially constant at the usual commercial levels,including less than 2.0% manganese, less than 0.75% silicon, and lessthan 0.30% nitrogen. Nitrogen and manganese can be substituted for partof the carbon or nickel in eflecting a balanced alloy. The nitrogenrange can extend from 0.003% to 0.30%. Elements commonly used forpurposes other than control of the magnetic properties may also bepresent in the alloy as, for example, titanium and/or columbium, inamounts ordinarily used for stabilization. Thus, titanium may be presentin amounts equivalent to four times the carbon content or upto about0.8%, and columbium may be present in amounts equivalent to eight timesthe carbon content or up to about 1.6%. Molybdenum up to 3% may be usedto improve corrosion resistance. These elements and the small content ofdeoxidizers and impurities, such as sulphur and phosphorus, normallypresent in commercial steels have been grouped together for purposes ofthis specification as "accessory elemen The sulphur and phosphoruscontents should be less than about 0.04% each.

The term accessory elements" as used herein and in the claims, thereforedesignates ingredients such as specified in the preceding paragraph,other than chromium, nickel, carbon, and iron, which may be present incommercial stainless steels.

A very suitable stainless steel alloy falls within the following rangesof percentages by weight:

Per cent Chromium 12 to 25 Nickel 5.5 to 14 Carbon 0.06 to 0.20Manganese Less than 2.00 Sulphur Less than 0.04 Phosphorus Less than0.04 Silicon Less than 0.75

Iron, balance and 19.5%, the nickel content should be higher mouse whenthe carbon content is lower and vice versa within the following limits:I

0.06 to 0.08% carbon-9.0 to 11% nickel 0.08 to 0.10% carbon-8.5 to 10%nickel 0.10 to 0.15% carbon-8.0 to 9.5% nickel 0.15 to 0.20% carbon-7.5to 9.0% nickel Giving effect to these relationships, we have found thefollowing narrower ranges to be preierred:

Per cent Chromium 17.5 to 19.5 Nickel 7.5 to 11.0 Carbon 0.06 to'0'.20

Iron, balance except for accessory elements In selecting a specificalloy composition within the above preferred range, if the carboncontent is on the low side, the nickel content should be on the highside, as indicated by the table showing the relationship between carbonand nickel contents. It is only where the chromium lies outside of therange of 17.5 to 19.5% that nickel outside of the range of 7.5 to 11.0%might be desirable, and in that case a low nickel content will be usedwith a high chromium content, and vice versa, but still within the broadrange first above given.

As a specific example, the following is given:

Example 1 The starting material was a rod of inch in diameter having thefollowing analysis:

Per cent Chromium 18.01 Nickel 8.63 Carbon 0.12 Manganese 0.52 Sulphur0.016 Phosphorus 0.017 1 Silicon 0.48

Iron, balance A rod of this analysis and of the diameter specified washydrogen annealed at between 1950 and 2050 F. for a sufiicient length oftime, usually a matter of seconds, to give it a dead soft anneal. Therod was then treated in a sequence of steps as follows:

If the last anneal in the foregoing sequence of steps is carried out ata temperature close to 1950 F., the record member so produced will haveresidual magnetism values lying on the curve AB of Figure 1 and coerciveforce values lying on the curve DF of Figure 2; whereas if the lastanneal is carried out at a temperature close to 2050 F., the recordmember so produced will have residual magnetism values lying on thecurve AC of Figure 1 and coercive force values lying on the curve DE ofFigure 2. These curves Draw to efiect a reduction of approximately andthe areas defined thereby will be more fully explained'hereina'fter.

Example 2 The starting material was a rod of inch diameter having thefollowing analysis:

Per cent Chromium Nickel Carbon Iron, balance except for accessoryelements The rod was subjected to the same sequence of steps as thosenumbered (1) through (8) of Example 1, but in step (9) was cold drawn toeffect a reduction of approximately 84% to produce a wire having adiameter of about 0.004 inch. With an applied field of 1000 gausses. thefinished wire showed a coercive force, He, of 300 and a residualmagnetism, Br, of 2400. A wire produced inthe same way except for afinal reduction of 77%, instead of 84%, showed an Hc of 300 and a Bl' of1700 with an applied field of 1000 ausses.

Example 3 The starting material was a rod of as, inch diameter havingthe following analysis:

Per cent Chromium 18.5 Nickel 8.8 Carbon 0.14

Iron, balance except for accessory elements The rod was subjected to thesame sequence of steps numbered as'(l) through (6) of Example 1,

-' but in step (7) was cold drawn to effect a reduction of approximately95% to produce a wire having a diameter of about 0.004 inch. With anapplied field of 1000 gausses, the so finished wire showed a coerciveforce, He, of about 300 and a residual magnetism, Br, of 1250.

Example 4 A inch rod was used "having the following analysis:

' Per cent Chromium 18.73 Nickel 9.06 Carbon 0.12

Iron, balanceexcept for accessory elements Using the same sequence ofsteps as steps (1) through (9) of Example 1, a wire of 0.004 inchdiameter was produced having an He of 265 and a Bl' of 1000 for anapplied field of 1000 gausses.

Example 5- The rod started with had the following analysis:

Percent Chromium 18.6 Nickel 9.4 Carbon 0.06

The-rod was-subjected to the same sequence of steps (1) through (9) ofExample 1 to produce a wire of 0.004 inch diameter having an He of 250and a Br of. 1000 with an applied field of 1000 gausses.

Example 6 The starting rod had the following analysis:

Per cent Chromium 17.87 Nickel 9.23 Carbon 0.105

Iron, balance except for accessory elements assasso The subjected to thesame sequence of steps (1) through (9) of Example 1 to produce a wire of0.004 inch diameter havingan m of 250 and a Br of 1500 with an appliedfield of 1000 gausses. g

' Example 7 a The starting rod had the following analysis:

. Per cent Chromium 18.67 me a 9.31 Carbon 0.085

Iron, balance except for accessory elements The rod was subjected to thesame sequence of steps 1) through (9) of Example 1 to produce a wire of0.004 inch diameter having an He of 250 and a B1- of 1200 with anapplied field of 1000 gausses.

In general, the dimensions of the rod or other blank used as thestarting material for our methdare unimportant. Originally, the alloy isin the form of an ingot. The ingot may be reduced to some suitabledimensions by any hot or cold forging operation. For wire. drawing,however, the starting point is usually a rod having a diam-' eter of Vinch or less.

In each of the foregoing examples the draw was eiiected at ordinary roomtemperatures, which, in general, would be from 15 to 30 C. and certainlybelow 50 0. While the upper limit of the temperature of the wire duringthe preliminary cold drawing steps is not particularly critical, thetemperature during the final reduction step should certainly be belowits transformation point, which is around 1200 F. in order to have themost favorable magnetic properties imparted to it as a result ofthefinal cold working step. The final reduction step should be a reductionin cross-sectional area to about 50 to 95%, and preferably about 65%.There should be no final annealing step after the final reduction stepsince if a sufiiciently high temperature is used to efiect a softanneal, the magnetic properties would be destroyed. It is possible toheat treat at a relatively low temperature, such as between 800 and 1200F., after the final reduction step without harming the magneticproperties of the wire, but we prefer to omit any final annealing stepentirely.

It will be understood that similar magnetic properties can be obtainedif, instead of cold drawing, the material is subjected to an equiv alentamount of cold forging, rolling, swaging or extruding. Where the finalform of the magnetic impulse record member is that of a circular wire,the diameter should be of the order of 0.004 inch and in any event lessthan 0.010 inch. In the case of ribbons, tapes or sheets, the thicknessshould be less than 0.010 inch and preferably of the order of from 0.001to 0.004 inch.

We have found that the'two most important magnetic properties to becontrolled in the magnetic impulse record member of our invention, areresidual magnetism and coercive force. In general, the record membershould be capable of reaching a residual magnetism of between 1000 and3000 gausses when the applied field is of the order of 1000 oersteds andshould be approximately saturated at that value for the applied field.Figure 1 shows limiting curves AB and AC representing maximum andminimum values of residual magnetism, Br, obtained by plotting residualmagnetism against the applied field, expressed in oersteds and denotedby H. The

resents values that have been found suitable in the case of magneticimpulse record members of our invention. While it will be understoodthat the curves AB and AC can be extended out to the right of the points3 and C, the extended portions of these curves would be substantiallyfiat and are therefore not significant. Accordingly, the area defined bythe curves AB and AC will be considered as the shaded area lying betweenthese curves and to the left of the ordinate joining the points B and C.

The slope of the curves AB and AC is particularly significant. As shown,for a relatively low intensity of applied field, as for instance a fieldbelow 100 oersteds. the residual magnetism is correspondingly low. Thisis very important,

since it means that for low applied field, the record member does notbecome appreciably magnetized. Consequently, the record member is noteasily magnetized by the proximity of magnetic fields of low intensity,as would be the case if there were a more nearly linear relationshipsuch as represented by the dot-dash line AB shown in Figure 1. Othermagnetic impulse record members that we have tested more closelyapproximate the slope of the dot-dash line AB for low intensity ofapplied field and are objectionable for that reason, since they tend tobecome magnetized by stray fields.

On the other hand, as the applied field increased in value aboveoersteds, the slope of the curves AB and AC rises quite steeply, so thatat fields of moderate intensity, say between 500 and 1000 oersteds,there is a corresponding substantial residual magnetism of the order ofbetween 1000 and 3000 gausses. These are values that are readilyobtained by the ordinary construction of recorder heads in magneticsound recorders.

Figure 2 shows in solid line two curves, DF and DE that represent thevalues obtained by plotting coercive force, He, against applied field,H, for magnetic impulse record members having a coercive force atsaturation within the desired limits of 200 to 300 oersteds. Since thecurves DE and DF intersect, as at K, two areas would, in fact, bedefined by these curves, but in order to include points plotted forvalues obtained in the testing of other satisfactory magnetic impulserecord members included in the foregoing examples, smooth compositecurves have been formed by joining the solid line portions DG and HE bya dotted line portion GH, and by joining the solid line curves DI and JFby a dotted line portion LI, and the area so included between compositecurves DGHE and DIJF has been shaded. This shaded area represents valuesfor coercive force that has been found satisfactory for magnetic impulserecord members of our invention.

It is preferable for ease of erasing the recorded magnetic impulses thatthe coercive force, He, of the record member be not over 300, but exceptfor this reason the coercive force could be higher. In general, withlower annealing temperatures, around 1950 F., higher residual magnetismvalues, Br, and lower coercive force values, He, are obtained. .Suchcontrol of the annealing temperature used, therefore, affords a way ofvarying these magnetic properties for the same composition of alloy.

As indicated by the curves on the drawings, the materialis practicallysaturated at fields of around 500. This makes for ease of erasing theshaded area between the curves AB and AC rep- :5 m n i ally recordedimpulses. esbecia y the use of a high frequency field, which has beenfound the most desirabietype of field to use from the standpoint of lownoise level.

In use, the magnetic impulse record members of our invention aremagnetized in accordance with the magnetic impulses which the membersare subjected. Our invention is therefore intended to include suchmagnetized record members.

As diagrammatically illustrated in Figure 3 of the drawing, the magneticimpulse record member II is arranged to have intelligence recordedthereon by passing the record member over a head l2 which varies themagnetic state of an incremental length of the record member H inaccordance with time variations of the intelligence. In reproduction,the record member H is again passed over the head l2 in the same.

direction and the condition or state of the record member along theincremental length thereof is reproduced as a signal, thereby convertingthe variations in the magnetic state of the record member along itslength to a time varying signal corresponding to the recordedintelligence.

A wide variety of apparatus has been developed in the past for effectingsuch operations, but the details of such apparatus form no part of thepresent invention One of the common systems includes transferring themagnetic impulse record member H from a storage reel l3 mounted on ashaft It to a -take-up reel l5 mounted on a shaft It. The shaft 18 maybe driven by any suitable source of power (not shown), and the shaft Itmay have a braking force applied in any suitable manner (not shown) toapply a slight tension to the impulse record member H as it passes firstover a demagnetizing head I! and then over the recording and play backhead l2. The demagnetizing head I] is for the purpose of uniformlydemagnetizing the magnetic impulse record member ll before a ma neticrecord is made thereon by the head l2. When an audible signal is to bemagnetically recorded on the traveling record member II, it

-is first converted by a microphone l8 into a fluctuating electriccurrent which is then amplified by an audio amplifier l9, and is thenfed through a switch 20 and an input circuit 2| to the head l2. A sourceof high frequency electric current such, for example, as the highfrequency oscillator 22, is connected to the erase head I! throughswitch 23 and an energizing circuit 2|. This conditions the recordmember ll immediately prior to recording by demagnetizing it. Highfrequency current from the oscillator 22 is also fed through switch 25and a. circuit 26 to the input circuit 2! of the recording head l2 tosuperimpose a high frequency bias current on the signal and therebyimprove the recording characteristics of the apparatus.

After a magnetic record is made on the record member ll by varyinglymagnetizing succeeding incremental lengths thereof, the member H isrewound onto the storage reel I! with switches 22 and 25 in their dottedline positions and with switch 20 in its intermediate open circuitposition. Thereafter, if it is desired to play back the record which hasbeen made on the record member II, the member II is again transferredfrom the storage reel H to the take up reel it, but this time theswitches 20, 23 and 25 are placed in their respective dotted linepositions so that no high frequency energy is fed to either 10 the erasehead I! or the recording and play back head i2. The varying magneticstate of the record member II induces an electric current in the signalcoil of the head l2, and this current is fed through the circuit 2| andthe switch 20 (in its dotted line position) through the circuit 28 tothe input side of the audio amplifier IS. The output of the audioamplifier is connected to a loud speaker 29 which converts thefluctuating electric signal current into an audible signal correspondingto the original signal previously recorded.

We claim as our invention:

1. The method of making a magnetic impulse record member, whichcomprises successively and repeatedly soft annealing at a temperature ofbetween about 1950 and 2050" F. and cold working a normally austeniticchromium-nickel alloy having an analysis within the followin percentagesby weight:

Per cent Chromium 12 to 25 Nickel 5.5 to 14 .Carbon 0.06 to 0.20

Iron, substantially the balance,

keeping the percentage of nickel low when the percentage of carbon ishigh and keeping the percentage of nickel low when the percentage ofchromium is high and vice versa within the above specified ranges, andeffecting a final cold work reduction of between 50 and incross-sectional area, with no subsequent annealing, to produce a memberhaving at least one dimension less than 0.005 inch and having a residualma netism, Br, for a given applied field, H, lying within the areadefined by the curves AB and AC and the ordinate joining the points Band C of Fig. l and a coercive force, He, for a given applied fleld, H,lying within the area defined by the curves DGHE and DIJF and theordinate joining the points E and F of Fig. 2 of the accompanyingdrawings.

2. The method of making a magnetic impulse record member, whichcomprises successively having an analysis within the followingpercentages by weight:

Per cent Chromium 12 to 25 Nickel 5.5 to 14 Carbon 0.06 to 0.20

Iron, substantially the balance,

keeping the percentage of nickel low when the percentage of carbon ishigh and keeping the percentage of nickel low when the percentage ofchromium is high and vice versa within the above specified ranges, andefiecting a final cold work reduction of between 50 and 95% incrosssectional area, with no subsequent annealing, to produce a wire ofcircular cross-section having a diameter of about 0.004 inch and havinga residual magnetism, Br, for a given applied field, H, lying within thearea defined by the curves AB and AC and the ordinate joining the pointsB and C of Fig. l and a coercive force, He, for

a given applied field, H, lying within the area defined by the curvesDGHE and DIJF and the ordinate joining the points E and F of Fig. 2 ofthe accompanying drawings.

3. The method of making a magnetic impulse Per cent Chromium. 17.5 to19.5 Nickel 7.5 to 11 Carbon 0.06 to 0.20

Iron, substantially the balance,

keeping the percentage of nickel low when the percentage of carbon ishigh and keeping the percentage of nickel low when the percentageofchromium is high and vice versa within the\ above specified ranges andefiecting a final cold work reduction of between 50 and 95% incrosssectional area, with no subsequent annealing, to

produce a member having at least one dimension less than 0.005 inch andhaving a residual magnetism, Br, for a given applied field, H, lyingwithin the area defined by the curves AB and AC and the ordinate joiningthe points E and F of Fig. 1 and a coercive force, He, for a givenapplied field, H, lying within the area defined by the curves DGHE andDIJF and the ordinate joining the points E and F of Fig. 2 of' theaccompanying drawings.

4. The method of making a magnetic impulse record member, whichcomprises successively and repeatedly annealing and cold drawing achromium-nickel-iron alloy having an analysis within about the followingranges of percentages by weight:

Per cent Chromium 17.5 to 19.5 Nickel 7.5 to 11.0 Carbon 0.06 to 0.20Iron, substantially the balance,

keeping the percentage of nickel toward the lower side of its specifiedrange when the percentage of carbon is toward the higher side of itsspecified range and vice versa, annealing within the temperature rangeof about 1950 to 2050 F. between successive cold drawing steps,eifecting a reduction in cross-sectional area of between about 50% and95% in the final cold drawing step without subsequent annealing toproduce a wire of circular cross-section having a diameter of the orderof 0.004 inch, and for the composition of alloy selected controlling thetemperature of the last anneal before the final cold drawing step andthe extent of the last cold reduction so as to impart to said wiremagnetic properties eminently suiting the same for use as a magneticimpulse record member, said properties including inappreciable residualmagnetism for an applied field below 100 oersteds but substantialresidual magnetism of the order of between 1000 and 3000 gausses forapplied fields of between 500 and 1000 oersteds and a coercive force atsaturation of at least 200 oersteds.

weight:

Per cent Chromium 17.5 to 19.5 Nickel 7.5 to 11.0 Carbon 0.06 to 0.20

Iron, substantially the balance,

keeping the percentage of nickel toward the lower side of its specifiedrange when the percentage of carbon is toward the higher side of itsspecified range and vice versa, annealing within the' temperature rangeof about 1950 to 2050 F. between successive cold working steps,effecting a reduction in cross-sectional area of between about 50% andin the final cold working step without subsequent annealing to produce amember having at least one dimension less than 0.005 inch, and for thecomposition of alloy selected controlling the temperature of the lastanneal before the final cold working step and the extent of the lastcold reduction so as to impart to said member magnetic propertieseminently suiting the same for useas a magnetic impulse record member,said properties including inappreciable residual magnetism for anapplied field below oersteds but substantial residual magnetism of theorder of between 1000 and 3000 gausses for applied fields of between 500and 1000 oersteds and a coercive force at saturation of at least 200oersteds.

MARVIN CAMRAS. HYRUM E. FLANDERS.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,915,766 Smith et al. June 27,1933 2,085,118 Noll June 29, 1937 2,114,183 Haase et al Apr. 12, 19382,167,188 Schaarwachter et al. July 25, 1939 FOREIGN PATENTS NumberCountry Date 463,901 Great Britain Apr. 8, 1937 482,037 Great BritainMar. 22, 1938 OTHER REFERENCES Book of Stainless Steels by Thum,published by the American Society for Metals, Cleveland, Ohio, 1935,pages 117-119, 372-373.

"The Alloys of Iron and Chromium," by Kinzel and Franks. volume 2,published by McGraw Hill Book Co., N. Y., 1938, pp. 338-340.

Journal of the Institute of Electrical Communication Engineers ofJapan," March 1938, pages 144-148.

